An important subsystem of an optical telecommunication system is the opto-electric interface which converts signals between the optical domain and the electrical domain. Typically, the opto-electric interface comprises some kind of opto-electric device (OED) for either transmitting or receiving optical signals. OEDs are commonly packaged in “TO can” assemblies which comprise a cap and a header assembly. The header assembly can be a hybrid microelectronic assembly which includes the OED plus one or more integrated circuits (ICs) or passive components.
In addition to the OED, a typical opto-electric interface comprises a printed circuit board or substrate containing the necessary circuitry to operate the OED, and a connector interface for interfacing with an optical connector of an optical fiber or cable. A typical optical connector comprises a housing with a ferrule disposed therein. The ferrule is configured to hold one or more fibers in a specific spacial relationship and has an end face which presents the fiber end(s). The end face is generally polished to provide for good optical contact with a mating face of the module. The combination of the fiber and optical connector is referred to herein as a “cable assembly”.
Generally, the OED, supporting circuitry, substrate and connector interface are packaged into a discrete module, referred to herein as an “opto-electric module” or just “module.” Opto-electric modules are generally configured for installation into larger host systems such as routers and computers. The modules are typically installed on host circuit boards within such host systems using conventional installation configurations such as through-pin mounting or pluggable receptacles. Since the modules are configured to interconnect to cable assemblies, the modules are typically positioned near the perimeter of the host system for accessibility and to avoid the need for circuitously routing the fiber through the host system. The desire to minimize the access area required for each module has lead to modules being elongated and rectilinear in shape such that they present an end face having a relatively small area for connection to the cable assembly.
Optoelectric modules tend to be expensive and there exists a need to reduce costs associated therewith. One way to reduce costs is to reduce waste during manufacture of the modules. Waste can be reduced by determining as early as possible in the manufacturing process whether the optical subassembly containing the OED is functioning properly. Early detection of a defective subassembly of the module can save costs that would have been incurred to complete the module, e.g. costs of additional assembly time and/or additional components. These costs are unnecessary if the OED component is defective and are avoidable if the defective nature of the OED is detected early.
For various reasons, prior art optoelectric modules are not compatible with early defect detection procedures. Specifically, prior art modules tend to require the assembly of numerous, difficult-to-assemble components to obtain a testable subassembly. For example, before testing of a prior art module can occur, typically the following components need to be assembled: an adapter for a connector, an OED, components for optically linking a connector to the OED, and control circuitry for the OED. Typically, these components represent the most expensive components of the module and require the most time and care to assemble. For example, the TO cans typically used in prior art modules are incompatible with most automated pick-and-place assembly operations and they lack reference surfaces to facilitate passive alignment. Therefore, TO cans must be handled manually and actively aligned by hand which is expensive and does not lend itself to high volume production. Therefore, TO cans increase the cost of the testable subassembly.
There is a need for an optoelectonic module having an optical subassembly that is readily testable before making a considerable investment of time and materials. The present invention fulfills this need among others.